Executive orders are instructions issued by the President to federal agencies that have the force of law. While they don't require Congressional approval, they are not a way for the President to "make" new laws entirely on their own.
The President's authority to issue executive orders comes from the Constitution and from laws already passed by Congress. They are usually used to manage the operations of the federal government or to direct how a specific law should be carried out.
Executive orders can be overturned in several ways:
Executive orders have been used for major historical actions, including Abraham Lincoln's Emancipation Proclamation and Harry Truman's integration of the U.S. military.